1. Field of the Invention
The present invention relates to methods and apparatus for fabricating corrugated paperboard. More particularly, the present invention relates to a method and corresponding apparatus for applying back pressure to a single-faced corrugated web while in transit over a glue applicator roll positioned for application of adhesive to the exposed flute tips of the single-faced assembly in preparation for adding a second liner web of a double-faced assembly.
2. Description of the Prior Art
In the fabrication of corrugated paperboard, a first liner web or single facing is adhesively applied to the flute tips of the corrugated medium web while the medium web is still in intimate contact with the corrugating roll surface profile. Consequently, the single-faced web may be positively pressed into intimate contact with the corrugation flute crests with a high pressure roll nip without concern for either crushing a portion of the corrugated web pattern by excessive contact pressure or omitting a flute line of adhesion because of insufficient contact pressure.
After the single-faced web is applied and the corrugated medium is stripped from the corrugated roll surface, the reverse face of the medium is no longer accessible to a corrugated backing profile in support of the medium for application of the double-facing web. Such absence of a positive backing support structure is particularly acute at the glue applicator station whereat adhesive for the double-facing web is applied to the exposed flute tips. Some pressure is required to hold the corrugated face of the continuously running, single-faced assembly firmly against the applicator roll surface to assure that sufficient adhesive is applied along the full transverse length of each passing flute tip. However, excessive pressure will crush the fluted web whereas insufficient pressure will permit skips in adhesive application.
Uncontrolled tendencies of a single-faced assembly to warp transversely represents a major source of difficulty in back pressure regulation. When a fixed dimension gap setting is used between the glue roll surface and a corresponding backing roll surface to transversely flatten a warped, single-faced board for line contact with the flute tip glue applicator roll, a line of crushed flutes often results along either the board center or along either edge.
A relatively recent prior art effort to control single-faced board back pressure at the double face glue station has been to mount a backing roll rotational axis along the approximate mid-span between two swing arms. One end of the swing arm is pivotally secured to the machine frame whereas the free ends of the arms are supported by fluid pressure. A fluid pressure control system supports substantially all of the roll weight applied against the single-faced board. Although a fluid pressure supported backing roll represents an improvement in board quality based on reduced skippage and flute crushing, significant latitude yet remains for further improvement.
It is therefore, an objective of the present invention to provide such further improvement in double-facer adhesive application.
Another objective of the present invention is to provide a method and apparatus for uniformly pressuring the exposed flute tips of a single-faced corrugated board against the adhesive applicator roll of a double-facer glue station but is also incapable of crushing the flutes with excessive pressure.